Using core lithology and palaeoecological analyses, the vegetational and landscape development and local hydrological conditions since c. 6000 BP in two areas of the Somerset Levels has been studied. Focusing on the former characteristics of the river Brue, the floodplain upstream from Glastonbury and the area near Panborough Gap in Wedmore Ridge were investigated. In the latter area a distinct palaeochannel thought to be the prehistoric course of the Brue is present. Both areas show a similar development with saltmarsh and lagoonal environments until 6000 BP, followed by a prolonged period of Alnus - Salix carr and sedge fens. In the Panborough area freshwater deposition was interrupted by distal saltmarsh and lagoon sedimentation between 2900 BP and 2200 BP. This marine incursion caused stagnation of river discharge upstream which led to the growth of Cladium-rich "tloodinq layers" in the central raised bog area. After embankment of the rivers in the Middle Ages the changed hydrological conditions caused deposition of the upper floodplain clays. Until medieval embankment and canalisation determined its present day course, the river Brue did not have a fixed course but consisted of several small short-lived channels. The palaeochannel in the Panborough area is filled with sediment from the Sheppey while its course is inherited from a tidal channel that was incised between 2900 BP and 2200 BP. Blocked by the raised bog in the west the Brue water took a northerly drainage route, and it seems likely that it contributed to this palaeochannel system. The Brue sediment however was deposited as floodplain and backswamp clays in the Glastonbury area, and the long-held opinion that the palaeochannel is the 'Old river Brue' therefore cannot be maintained. Processes in the coastal region have been inferred from the local hydrological changes and these inferences have partly been verified with a simplified, two-dimensional hydrogeological model.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:297642 |
| Date | January 1999 |
| Creators | Aalbersberg, Gerard |
| Publisher | University of Exeter |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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